Preheat oven to 350°F (180°C). Meanwhile, in bowl whisk eggs with milk, salt and pepper until smooth. Stir in onion and sausage mixture, sweet potato and Cheddar. Wipe skillet clean with paper towel. Add remaining oil and set over medium heat. Pour frittata mixture in skillet. Cook 5 min., or until eggs start to set on the bottom and around edges.

Transfer to oven for 13 to 15 min. or until eggs are set. Cut into wedges and serve with green salad.